1. Field of the Invention
The present invention pertains to an in-the-hole hydraulically actuated percussion tool particularly adapted for drilling relatively small diameter blastholes and for use in subterranean well operations.
2. Background
There have been several developments in the design of reciprocating piston-hammer type percussion tools wherein the energy output of the tool has been improved by utilizing hydraulic fluids as the working pressure fluid in order to provide for higher effective working pressures of the fluid and to increase the rate of energy output of the tool. U.S. Pat. Nos. 3,903,972; 3,896,889; and 3,991,655 to J. V. Bouyoucos describe examples of one type of hydraulic impact tool wherein a reciprocating piston-hammer actuates a sleeve type fluid distributing valve in both directions of hammer movement. U.S. Pat. No. 4,474,248 to Musso also describes a hydraulic impact tool wherein the piston-hammer is reciprocated through a working stroke cycle by actuation of a sleeve type fluid distributing valve which is moved in opposite directions by pressure fluid forces. Still further examples of hydraulic impact tools are described in U.S. Pat. Nos. 4,109,734 and 4,165,788 to Roger Montabert.
In the further development of hydraulic impact or percussion type tools certain improvements have been sought, particularly giving consideration to minimizing the overall outside diameter of the tool for certain applications which require a relatively slender in-the-hole tool or drill. It is, for example, desirable to avoid an arrangement where the fluid distributing valve encircles the piston-hammer while still providing for low pressure loss of the working fluid during the valving action. Other considerations include the location and type of pressure fluid accumulator which can be effectively utilized without increasing the overall tool diameter. Still further considerations include the provision of a hydraulic percussion impact tool or rock drill which can utilize a working fluid which is discharged into the borehole to serve as a cuttings evacuation fluid and dust suppressant. The use of water and fluids known as drilling muds are desirable to use in certain applications and tools using such fluids also enjoy the advantage that the construction of the tool may be such that it does not require fluid return passages nor are fluid return conduits required to be connected to the tool.
With the above objectives in mind and including other desired features in hydraulic percussion tools for drilling relatively small diameter holes the present invention has been developed and has met the criteria mentioned herein as well as providing for other unique advantages.